Conventional guardrail assemblies installed along highways typically have at least one horizontal guardrail that is supported at spaced locations by vertical posts anchored in the ground. Generally the guardrail sections are heavy gauge sheet metal formed into a W-shaped corrugated section. Guardrails are constructed of individual sections joined in end to end relationship and overlapping at the vertical posts where they are connected with bolts. The corrugation of the W shape imparts rigidity and strength to the guardrail while being relatively simple to fabricate.
Metallic guardrails are specificly designed to yield when impacted upon by a colliding vehicle. The deformation of the sheet metal guardrail serves to decelerate the vehicle and guide the vehicle away from hazards such as slopes, signs or oncoming traffic. Increasingly however the cost of maintaining sheet metal guardrails after impact has created a demand for a flexible guardrail which can decelerate impacting vehicles while reducing the cost of maintenance by remaining substantially intact after impact.
In addition metallic guardrails made of steel are subject to rapid deterioration due to corrosion from constant exposure to precipitation, salt and stones. In order to prevent deterioration of the guardrails, the steel surfaces are generally galvanized with zinc. However, flying stones and other debris thrown against the guardrail by passing vehicles or high winds can cause pitting of the surface and permit corrosion to rapidly deteriorate the exposed the steel surfaces. Therefore highway guardrails are often unsightly even if not particularly damaged by impacting vehicles.
Especially in areas such as curves or high traffic concentrations, maintenance of guardrails becomes an expensive and time consuming process. On busy highways and around curves on entrance and exit ramps constant maintenance may be required in order to keep the metal guardrails in safe and operable condition.
The prior art therefore includes a number of covers which are attached to existing guardrails to offer a resilient surface and to rehabilitate the appearance of the deteriorated guardrails. Examples of rubber covers which are bolted to or integrally formed onto sheet metal guardrails are disclosed in French patent publication no. 2460365 published Jan. 23, 1981--Societe Civile D'Equipement Public and Swiss patent No. 618488 dated Jul. 31, 1980.
A significant disadvantage of both such prior art devices is that the rubber cover closely follows the contours of the underlying sheet metal guardrail. The relatively thin cover of rubber is insufficient to absorb the impact of a vehicle colliding with the barrier at normal highway speeds. After such a collisions both the rubber cover and sheet metal guardrail must be completely replaced. The relatively thin cover layer of rubber would simply peel off due to the force of a vehicle scraping along the composite guardrail. Therefore, thin layers of rubber covers are ineffectual in preventing damage to the metal guardrail, are insufficiently flexible to prevent damage to the impacting vehicle and appear to merely represent an attempt to rehabilitate the appearance of the sheet metal guardrail.
German patent No. DE 4135164A1 dated Jan. 28, 1993 discloses a flexible rubber guardrail cover which is relatively thin such that it may be coiled in cylindrical rolls. The guardrail cover rebounds to a C shape when uncoiled during installation to wrap around an existing guardrail. Such a cover is insignificant in protecting the guardrail structure and would merely peel off when impacted by a colliding vehicle. The primary purpose of such a thin cover would appear to be economical and rapid rehabilitation of the appearance of an unsightly guardrail.
Therefore it is desirable to produce a guardrail adaptor which may be easily snap-fit over an existing guardrail while also providing a substantial degree of protection from impacting vehicles for the guardrail.
It is also desirable to produce a resilient guardrail adaptor which will not simply peel off the guardrail when impacted by a colliding vehicle.
The danger of dispersing guardrail materials over the travelled surface of a busy highway presents significant disadvantages since such debris may cause additional accidents and delays on the highway. It is desirable therefore that, on impact with a colliding vehicle, the sheet metal guardrail and the rubber adaptor remains substantially intact.